In a small saucepan, combine lemon juice, lemon zest, egg yolks, granulated white sugar, and salt. Whisk together until smooth.

Heat over medium-low heat, stirring frequently, until the mixture thickens, about 20-25 minutes. It should coat the back of a spoon when ready.

Remove from heat and whisk in the cold, cubed butter until fully melted.

Transfer the lemon curd to a medium heatproof bowl. Cover with plastic wrap, pressing it directly onto the surface to prevent a skin from forming. Let it cool completely.

In a small bowl, whisk together the flour, baking powder, and salt.

In a large bowl, cream the softened butter and granulated white sugar with an electric mixer on high speed until fluffy, about 2-3 minutes. If using a stand mixer, use the paddle attachment.

Add the egg yolk, vanilla extract, and lemon zest. Mix on medium-high speed until pale and fluffy, about 1-2 minutes.

Gradually add the dry ingredients, mixing on low then medium speed until combined. Scrape the sides of the bowl as necessary.

Scoop the dough into 1-tablespoon portions and roll into balls. Press each ball with a ½ teaspoon to make an indent.

Chill the prepared dough balls on parchment paper-lined baking sheets for 1 hour.

Preheat the oven to 350°F.

Place 12 chilled cookies on a parchment paper-lined baking sheet.

Bake for 9-10 minutes.

Immediately after baking, use a small, round cookie cutter to gently reshape the cookies, if necessary. Press the centers again with a ½ teaspoon to deepen the indent.

Let the cookies cool on the baking sheet for 5 minutes, then transfer to a cooling rack to cool completely.

Once cooled, spoon about 1 teaspoon of lemon curd into the center of each cookie. Optionally, sprinkle with powdered sugar before adding the lemon curd.